The semiconductor manufacturing industry has long been focused on the miniaturization of microelectronic devices. One strategy that has been used to continue the miniaturization trend is known as silicon-on-insulator, or SOI. This technique uses a substrate having an electrically insulating layer in between layers of silicon as a means to improve performance due to, for example, the reduction of the short channel effect (SCE) and parasitic device capacitance. In addition, the floating body effect from the isolated channel enables us to use the device on SOI as a memory device. On the other hand, SOI technology does have certain limitations, such as those that arise as a result of the difficulty in controlling film thicknesses, resistances, and other parameters. As device scaling continues to advance these limitations will become increasingly problematic. SOI substrates also have higher manufacturing costs than bulk silicon substrates.
Silicon-on replacement insulator (SRI) technology (sometimes also called silicon-on-nothing, or SON) is in many respects a way of overcoming the limitations of SOI. In SRI technology, a silicon film is epitaxially grown on a sacrificial silicon germanium (SiGe) layer that when removed, leaves an air gap under the film that will later be replaced with an insulator. Yet the SRI process comes with its own set of issues, including silicon corrosion in the unprotected source/drain (S/D) regions and degradation in selectivity during SiGe removal etching. For example, it has been found that plasma damage on silicon exposed to an oxide dry etch process can cause top silicon loss during SiGe etching.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the discussion of the described embodiments of the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Similarly, if a method is described herein as comprising a series of steps, the order of such steps as presented herein is not necessarily the only order in which such steps may be performed, and certain of the stated steps may possibly be omitted and/or certain other steps not described herein may possibly be added to the method. Furthermore, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner. Objects described herein as being “adjacent to” each other may be in physical contact with each other, in close proximity to each other, or in the same general region or area as each other, as appropriate for the context in which the phrase is used. Occurrences of the phrase “in one embodiment” herein do not necessarily all refer to the same embodiment.